Vacuum switch



Dec. 19, 1961 J- D. COBINE ET'AL VACUUM SWITCH In venfors James 0.Cob/he,- Emmef/ 5 Burger,

The/r Attorney United States Patent ()fiice 3,014,108 Patented Dec. 19,1 961 3,014,108 VACUUM SWITCH James D. Cobine, Rexford, and Emmett E.Burger, Schenectady, N.Y., assignors to General Electric Company, acorporation of New York p Filed Jan. 2, 1959, Ser. No. 784,745

7 Claims. (Cl. 200-144) Our invention relates to an improved alternatingcurrent vacuum switch mechanism of the type in which acircuit-interrupting arc is maintained by vaporized electrode materialsubstantially until current zero before interruption.

In vacuum type switches an envelop, partially or totally fabricated fromglass or other suitable insulating material, forms a vacuum cavity inwhich a pair of relatively movable electrodes are located. In oneposition of the electrodes, direct conducting contact is made betweenthem tocarry the current flow of the circuit to which the switch isconnected. In a second, circuit-opening position, the electrodes arespaced and no current flows therebetween. It is the function of theswitch to transfer from the circuit-making to the circuit-openedcondition in reliable fashion, assuring that the current flow ispromptly interrupted and yet no excessive overvoltages occur in theconnected circuits. To this end, it is important that the current flowbe maintained in'the switch until the alternating current wouldotherwise fall to zero, thus assuring that there is no sudden currentinterruption to create circuit overvoltages. In addition, long life andreliability demand-that the unit be so constructed that the electrodeerosion associated with arcing action is minimized and the deposit ofconducting electrode material on the inside walls is likewise minimized.

V In the switch herein described, the electrodes are in the form oftelescoping members that define an elongated annular space. In thecontact-making position of the electrodes, a current-carrying path isdefined between the end of the inner electrode and the base of thecavity of the outer electrode. When the inner electrode is withdrawn, anarc is struck at or near the surface of initial contact. The unit isoperative to cause the are so struck to travel toward the open end ofthe cavity under the influence of variations in the length of the arcinggap, and magnetic interaction. This are travel, coupled with theinfluence of a magnetic field in the longitudinal direction of theannular space thereupon, gives rise to a spiral path of movement of thearc away from the base of the cavity and towards the opening thereof.The length of the cavity is sufficient to assure that at least asubstantial .portion of the time to the next occurring current zeropasses before the arc reaches the opening of the cavity. Since the arcis in continuous movement and traverses a substantial portion of theelectrode area, the eroding effect of the are on the electrode materialis distributed and the electrodes have long life before undue erodingoccurs. Moreover, the space in which the electrode material is vaporizedis largely surrounded by the electrodes themselves (at least during mostof the arcing period) and relatively small quantities of vaporizedelectrode material escape into the vacuum space proper to deposit on theinsulating walls thereof.

' It is therefore an object of the present invention to provide animproved vacuum-type switch in which relatively movable telescopingmembers coact with a magnetic field to impart a spiral movement of thearc until current zero is reached.

Another object of the present invention is to provide 'an improvedalternating current vacuum switch mech- -anism' in which relativelymovable telescoping members define "an annular space of decreasing arcresistance as the arc moves away from the initial contact-makingportions, and a magnetic field imparts spiral movement to the are as ittravels in response to the decreasing arc resist ance.

It is still another object of the present invention to provide animproved alternating current vacuum switch construction in which theaction of axial and circumferential magnetic fields serves to impart aspiral-like travel to the are upon circuit opening.

Yet another object of the present invention is to provide an improvedvacuum switch mechanism for use in alternating current circuits andhaving features of con: struction, combination and arrangement thatprovide a simple, readily manufactured, highly reliable, long life unitthat is especially suitable for use in commercial circuit breaking orswitching applications and can be modified to varying forms toaccommodate a wide range of circuit conditions and performancerequirements.

The novel features which we believe to be characteristic of ourinvention are set forth with particularity in the appended claims. Ourinvention itself, however, together with further objects and advantagesthereof, will best be understood 'by reference to the followingdescription taken in conjunction with the accompanying drawing in which:7'

FIG. 1 is an axial cross-sectional view with parts in elevation of aswitch constructed in accordance with the present invention andincorporating permanent magnet elements within the vacuum space;

FIG. 2 is a fragmentary view generally like FIG. 1 but showing a switchwith solenoid means to create a circumferential magnetic field; and

FIGS. 3 and 4 are fragmentary enlarged cross-sectional views throughaxes 33 and 4-. 4, of FIG. 2, respec-. tively.

Referring now to FIG. 1, there is provided an insulating envelop 10defining a generally cylindrical vacuum space indicated at 12.. Theenvelop 10 may, for example, be of glass, although other vacuum tightinsulating materials may be used. At end 10a the envelop 10 receives theshank portion 14a of the outer and fixed electrode 14. The shank portion14a of electrode 14 is of a conducting material that adheres tightly tothe envelop material to prevent passage of air therebetween, at least inthe portions embedded in the envelop 10. At the opposite end 10b, theenvelop 10 embeds the peripheral portion of the disk 16a of the bellows16,- gain forming a vacuum-tight joint. Bellows 16 forms a relativelymovable but vacuum-tight structure embracing the shank portion 18a ofthe movable electrode 18.

Suitable means (not shown) are provided to move the movable electrode 18between the dotted line position of FIG. 1 and the solid line positionshown. In the former position, the electrodes 14 and 18 are in physi calcontact at seating faces 18c and1 4f to conduct current. In the latterposition they are spaced and, after current interruption, areelectrically disconnected.

The shank 14a of the fixed electrode 14 forms a conducting supportingdisk 14b within the vacuum space 12. This disk is aflixed to andreceives the arcing electrode portion, indicated at 140. As shown, thisportion is of cup shaped conformation having a cylindrical outer surfaceand an elongated longitudinal cavity. This cavity has an opening 14dthrough which electrode 18 extends,

I As shown, the inner electrode 18 is telescopically positioned withinthe cavity formed by electrode .14. Elec- 3 trode 18 includes anelongated truncated conical head portion 18b afiixed to the shankportion 18a and is of smaller diameter toward the base 14a of the cavityin electrode 14. The head portion of electrode 18 is beveled at 180 tomake contact with the lip 14 of electrode 14, as shown.

The cavity of the electrode 14 and the head portion 18b of the electrode18 coact to define an elongated annular space 20. In the structureshown, this space is of circular cross-section and increases incross-sectional area toward base 14c of the cavity in electrode 14. Ashereinafter described, the are associated with current interruptionspirally travels within this space and away from the base 14c untilcurrent zero is reached.

The cup portion 140 of the electrode 14 receives the jacket 22. This isof permanent magnet material, such as an Alnico alloy and is magnetizedto produce one permanent magnet pole at end 22a and a magnet pole ofopposite polarity at end 22b. The resulting magnetic field at theannular space 20 is in the longitudinal direction of this space, thatis, in the direction of the axis of symmetry of the cavity of electrode14 and the head portion 18b of the electrode 18, and the direction ofmovement of electrode 18.

If desired, the magnet sleeve 22 may be replaced by a solenoid or aseries of bar magnets distributed about the periphery of the electrodeportion 140 and forming elements of the cylinder defined thereby.Chamber 12 within envelop is maintained at a pressure of less than lOmm. of mercury in order that gaseous ionization be substantially absent.

The headed portion 18b of electrode 18 and the cavitydefining portion140 of electrode 14 are of a conducting material capable of vaporizationto form conducting ions within the space 20. Materials of this kind aredescribed in Lee and 'Cobine patent application SN. 750,784, filed July24, 1958, assigned to the same assignee as the present invention.Suitable materials include tin, antimony, lead, zinc, manganese,bismuth, and alloys thereof, as well as conventional electrode materialssuch as copper, aluminum, and alloys thereof. These materials arerefined in vacuo to remove all sorbed gases as set forth in the Lee andCobine application to prevent the pressure within the switch from risingwith repeated use.

The cavity formed by electrode 14 and the headed portion 18b ofelectrode 18 are so shaped that they define an annular space havingdecreased arc resistance as the opening 14d is approached. This makesthe are formed at or near the contact-making surfaces 14] and 180 travelaway from these surfaces and towards the opening 14d. The actual rate ofarc movement is determined by the magnetic, electrical, and thermaleffeats of the arc current itself and by its interaction with thelongitudinal magnetic field within the electrodes and the annular space20. In general, the arc tends to seek the shortest span across theannular gap 2% and for this reason the necessary motion is readilycontrolled by forming the head portion 18b of movable electrode 18 witha conical shape as shown. Alternatively, electrode 18 may be cylindricaland electrode 14 conical toward end 14d. Normally this is sufficient tocause the requisite axial arc travel. As hereinafter described in moredetail with respect to the construction of FIG. 2, this motion may alsobe accomplished by the coaction of the longitudinal magnetic fieldwithin the annular space 20 and a circumferential magnetic field thereinindependently of electrode shape. The essential point is that the are,initiated at the contact-making surfaces 180 and 14 tends to travel awayfrom these surfaces in a spiral-like motion.

The longitudinal magnetic field within the annular space 29 causes thearc to rotate therein. This is due to the coaction of the magnetic fieldof the radial arc itself, and the longitudinal magnetic field. The aretends to move in a direction at right angles both to the magnetic fieldand its own direction of current flow, thus giving a circumferentialdirection of movement and rotation of the are about the space 20.

It will be observed that the combined effect of the rotation of the areunder the influence of the longitudinal magnetic field in annular space20 and the movement of the arc towards the opening 14a is that ofimparting a spiral motion to the are as it travels away from thecontact-making surfaces 14 and 18c. The length of the annular space 20is preferably made sufficient to assure that a current zero is reachedbefore the arc reaches the opening 14d. For example, in a sixty cyclecircuit, the length of the space 20 is made greater than thelongitudinal distance the arc travels in second, thus assuring thatregardless of the instant the electrodes separate, there is ample timefor the current zero to be reached before the arc reaches the opening14d. This distance, of course depends upon the current interrupted andthe value of the longitudinal magnetic field and may readily bedetermined.

It is not essential, however, that the axial length of annular space 20absolutely exceed the longitudinal distance the arc travels in half thealternating current cycle. The statistical prospect of requiring a fullhalf cycle to the next occurring current zero is small and the arecurrent falls as it approaches the Zero point. For these reasonsadequate performance may be achieved by relying upon the arc rotatingabout opening 14g to carry the low current existing just prior to thecurrent zero condition when the electrodes separate under the mostadverse condition. The cavity 20 may thus be made somewhat shorter thanthat corresponding to one half cycle.

It will be noted that the arc is in continuous motion during thecircuit-opening operation and that such motion is symmetrical about theaxis of the electrodes. Consequently the erosion associated with the arcaction on the electrode materials is distributed over considerableelectrode area and at no time does the arc dwell at particular electrodepoints to heat and erode the same excessively. Moreover, since the arcis initiated at the base end of the cavity, the vaporized electrodematerial is located deep in the cavity and tends to deposit on theelectrodes themselves rather than escaping through opening 14d tocondense on the insulating walls of the envelop 10. If desired, theaxial length of the annular space 20 may be increased over the lengthdictated by considerations of the alternating current frequency andlongitudinal magnetic field strength to decrease the amount of vaporizedelectrode material so escaping. Alternatively, one or more disk-shapedbaffles, or their functional equivalents, may be located near opening14:1 to prevent loss of electrode material by evaporation andcondensation.

FIGS. 2-4 are fragmentary views of a vacuum switch constructed inaccordance with an alternative embodiment of the present invention. Inthis construction, the evacuated envelop defines vacuum space 112 and atits end 110a embeds and supports the shank 114a of the fixed electrodeunit indicated generally at Hz. This unit includes an electrode proper,indicated at 114e, which defines a cavity having end opening 114d. Aninsulated spacer disk 114d supports the electrode proper from thesupport disk 11412 and is attached to electrode proper 114a and supportdisk 11% by suitable insulated bolts or other fasteners (not shown). Asuitable conductor 114 is aflixed and electrically connected to disk11417. This conductor makes at least one turn about the magnetic core124a as shown, and is afiixed and electrically connected to the base endof the electrode proper 1140. The magnetic core 124a has two upstandingarms 124b extending up the side of the fixed electrode 1140 as shown.

The movable electrode 118 has a head portion 118b similar to 13!), FIG.1, but with a cylindrical lateral surface. This head portion has abeveled end at 1180 which coacts with the beveled seat 114 of the fixedelectrode proper, 14c.

distance from the outer face of the electrode 114 to form an annularcontact surface for normal current conduction. A solenoid winding 122 iswrapped about the envelop 110 in the region of the annular space definedby electrodes 114and 118 and is energized by suitable D.-C.voltagesource 122a to provide a longitudinal magnetic field in theannular space 120.

In the apparatus of FIGS. 2-4, the current flow between the electrodes114 and 118 passes from the shank 114a to the disk 114b and thence byconductor 1141' about the core 124a. This current creates amagnetomotive force along the length of core portion 124a andaccordingly a magnetic field between the arms 124b. This field fringesas shown by the dashed line 125, FIG. 3, to extend in a generallycircumferential direction across one side of the annular space 120. Thefield is accordingly located substantially along one element of thecylinder defined by the annular'space 120. When the arc is within thisfield, it is driven by magnetic action towards the opening 114d of thecavity in electrode 114a. Since the direction of the field is determinedby the direction of the current flow through conductor 114 the properrelationship between field orientation and currentflow always exists todrive the arc towards opening 114d. The effect of this field(exemplified by line 125, FIG. 3) is to shiftthe are some axial distancetowards the opening 114d on every full circumferential movement aboutthe annular space 120. The field of the winding 122 accordingly coactswith the circumferentially directed field (exemplified by line 125, FIG.,3) to impart spiral-like movement of the arc and thereby achieve actionsimilar to. that achieved solely through the electrode configurationin-the embodiment of FIG. 1. This electrode configuration may also beused in this embodiment to fortify the magnetic action described herein.

The core 124 is preferably made of a laminated magnetic material.Silicon steel may, for example, be used. The conductor 114i and the core124 are separated by suitable insulating barrier (not shown) at theirareas of .contact to assure full current flow through this conductor. Ifdesired, the electrodes 114 and 118 may be provided with auxiliarycontact-making faces to bypass the con- .ductor 114 under normal currentcarrying conditions.

In FIG. 2, it will be noted that the magnet 22 is located wholly withinthe vacuum space and does not .extend' closer to movable electrode 18than the fixed Since the vacuum space is a highly effective insulatingmedium, this location of the magnet has the advantage of maintaining thefull insulating path defined between the electrodes 14 and 18 by theoutside face of the envelop 10. If desired, the winding 122, FIG. 2, mayhave a greater radius than is shown in FIG. 2 to space the conductorthereof some envelop and thereby minimize the chance of externalbreakdown along the outside face of envelop 10 andthrough the winding.

In-the appended claims the electrodes are referred to as being so shapedthat in the circuit-opening position the arc travels towards the mouthof the cavity in the outer electrode. The actual arc movement isprimarily the result of magnetic effects and interactions. By thislanguage we intend to define a shape of the electrodes such that inconjunction with these effects the arc moves as described. In variousconstructions, of course, the actual shapes of the'electrodes may bedifferent from those in. other applications due to the variations inthese mag netic effects.

' While we have shown and described specific embodiments of the presentinvention it will, of course, be

understoodthat various modifications and alternative constructions maybe .made without departing from the true spirit and scope thereof. Wetherefore intend by the appended claims to cover all such modificationsand alternative constructions as fall within their true spirit andscope.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An alternating current vacuum switch mechanism of the type in which acircuit-interrupting arc is maintained by vaporized electrode materialsubstantially to current zero before interruption, the mechanismcomprising in combination: means defining a vacuum space; a firstelectrode extending through saidmeans to define a first circuit terminaloutside said space, said electrode defining a cavity having a base andan open end within said space, the base of said cavity having acentrally located secondary bore defining an annular lip at its junctionwith the base; a second electrode telescopically received in said cavityand extending outside said space to define a second circuit terminaloutside said space, said second electrode forming an elongated annularspace in relation to said first electrode; said electrodes being movablerelative to each other in the longitudinal direction of the annularspace, said movement being between a first position in which theelectrodes are in contactmaking relationship at said lip and a secondposition in which said electrodes are out of contact, the electrodesbeing so shaped that the radial distance between the electrodes isgreater at the closed end of said annular cavity than at the open endthereof so that when the electrodes are in said second position an arctherebetween travels towards the open end of said cavity; and meanscreating a magnetic field longitudinal of said annular space, the lengthof said annular space being greater than at least a major portion of thedistance the arc travels in a half cycle, whereby as the electrodes aremoved from the first position to the second position the arc is struckat said lip and spirals towards the open end of the cavity untilsubstantially current zero.

2. An alternating current vacuum switch mechanism of the type in which acircuit-interrupting arc is maintained by "aporized electrode materialsubstantially to current zero before interruption, the mechanismcomprising in combination: means defining a vacuum space; a firstelectrode extending through said means to define a first circuitterminal outside said space, said electrode defining a cavity having abase and an open end with said space; a second electrode telescopicallyreceived in said cavity and extending outside said space to define asecond circuit terminal outside said space, said second electrodeforming a longitudinal annular space in relation to said firstelectrode; said electrodes being movable relative to each other in thelongitudinal direction of said annular space, said movement beingbetween a first position in which the electrodes are in contactrnakingrelationship at the base of said cavity and a second position in whichsaid electrodes are out of contact, the electrodes being so shaped thatthe radial distance between said electrodes is smaller at the open endof said cavity than at the closed end thereof so that when theelectrodes are in said second position an arc therebetween travelstowards the open end of said cavity; the length of said annular spacebeing greater than at least a major portion of the distance the arctravels in a half cycle, and means creating a magnetic field lengthwiseof said annular space, whereby as the electrodes are moved from thefirst position to the second position the arc is struck at the base ofthe cavity and spirals towards the open end thereof until substantiallycurrent zero.

3. An alternating current vacuum switch mechanism of the type in which acircuit-interrupting arc is maintained by vaporized electrode materialssubstantially to current zero before interruption, the mechanismcomprising in combination: means defining a vacuum space; a firstelectrode having at least portions within said space and of elongatedcup shaped conformation with a cylindrical outerwall and an elongatedcavity having a base; a second electrode telescopically received in saidcavity and defining a longitudinal annular space in relation to thefirst electrode; said electrodes being movable relative to each other inthe longitudinal direction of the annular space, said movement beingbetween a first position in which the electrodes are in contact-makingrelationship at the base of said cavity and a second position in whichsaid electrodes are out of contact, the electrodes being so shaped thatthe radial distance between said electrodes is greater at the open endof said cavity than at the closed end thereof so that when theelectrodes are in said second position the arc travels towards the openend of said cavity; and a permanent magnet sleeve embracing the firstelectrode and magnetized in the longitudinal direction of the annularspace to create a magnetic field in said annular space in thelongitudinal direction thereof, the length of said annular space beinggreater than at least a major portion of the distance the arc travels ina half cycle, whereby as the electrodes are moved from the firstposition to the second position the arc is struck at the base of thecavity and spirals towards the open end thereof until substantiallycurrent zero.

4. An alternating current vacuum switch mechanism of the type in which acircuit-interrupting arc is maintained by vaporized electrode materialssubstantially to current zero before interruption, the mechanismcomprising in combination: means defining a vacuum space; a firstelectrode having at least portions within said space and of elongatedcup shaped conformation with a cylindrical outer wall and an elongatedcylindrical cavity having a base; a second electrode telescopicallyreceived in said cavity and of conical conformation to define anelongated annular space with respect to said cavity and having graduallyincreasing cross-sectional area as the base of the cavity is approached;said electrodes being movable relative to each other in the longitudinaldirection of said annular space, said movement being between a firstposition in which the electrodes are in contact-making relationship atthe base of said cavity and a second position in which said electrodesare out of contact; and a permanent magnet sleeve embracing the firstelectrode and magnetized in the longitudinal direction thereof to createa magnetic field in said annular space in the longitudinal directionthereof, the length of said annular space being greater than at least amajor portion of the distance the arc travels in a half cycle whereby asthe electrodes are moved from the first position to the second positionthe arc is struck at the base of the cavity and spirals towards the openend thereof until substantially current zero.

5. An alternating current vacuum switch mechanism of the type in which acircuit-interrupting arc is maintained by vaporized electrode materialssubstantially to current zero before interruption, the mechanismcomprising in combination: means defining a vacuum space; a firstelectrode having at least portions within said space and of elongatedcup shaped conformation defining a cavity said space having a base andopen end within said space; a second electrode telescopically receivedin said cavity and of tapering conformation to define an elongatedannular space with respect to said cavity and having gradually increasedcross-sectional area as the base of the cavity is approached saidelectrodes being movable relative to each other in the longitudinaldirection of said annular space, said movement being between a firstposition in which the electrodes are in contact-making relationship atthe base of said cavity and a second position in which said electrodesare out of contact; and means creating a magnetic field longitudinal ofsaid annular space, the length of said annular space being greater thanat least a major portion of the distance the arc travels in a half cyclewhereby as the electrodes are moved from the first position to thesecond position the arc is struck at the base of the cavity and spiralstowards the opening thereof until substantially current zero.

6. An alternating current vacuum switch mechanism of the type in which acircuit interrupting arc is maintained by vaporized electrode materialssubstantially to current zero before interruption, the mechanismcomprising in combination: means defining a vacuum space; a firstelectrode having at least portions within said space and defining anelongated cavity with an open end and base; a second electrodetelescopically received in said cavity and defining a longitudinalannular space in relation to the first electrode; said electrodes beingmovable relative to each other in the longitudinal direction of theannular space, said movement being between a first posi tion in whichthe electrodes are in contact-making relationship at the base of saidcavity and a second position in which said electrodes are out ofcontact; means including a conductor in circuit with said electrodeswhen in said second condition defining a circumferential magnetic fieldalong at least an element of said annular space, whereby an arc is movedtowards said open end when under the influence of said field; and meansto create a magnetic field longitudinal of said annular space to rotatethe arc circumferentially about the annular space and repeatedly throughthe zone of influence of the circumferential magnetic field, the lengthof said annular space being greater than at least a major portion of thedistance the arc travels in a half cycle, whereby as the electrodes aremoved from the first position to the second position the arc is struckat the base of the cavity and travels on a spiral-like path towards theopen end thereof until current zero.

7. An alternating current vacuum switch mechanism of the type in which acircuit-interrupting arc is maintained by vaporized electrode materialsubstantially to current zero for interruption, the mechanism comprisingin combination: means defining a vacuum space; a first electrodeextending through said means to define a first circuit terminal outsidesaid space, said electrode defining a cavity having a space and an openend within said space, the base of said cavity having a centrallylocated secondary board defining an annular lip at its junction with thebase; a second electrode telescopically received in said cavity andextending outside said space to define a second circuit terminal outsidesaid space, said second electrode forming an elongated annular portionin relation to said first electrode; said electrodes being movablerelative to each other in a longitudinal direction along the annularspace, said movement being between a first position and in which theelectrodes are in contact-making relationship at said lip and a secondposition in which said electrodes are out of contact; means for causingan are which exists between said electrodes in said second position tobe impelled from the base end of said cavity to the open end thereof;and means creating a magnetic field longitudinal of said annular space,said magnetic field being elfective to cause said are to rotatecircumferentially around said annular space under the influence thereof,the sum total of the motions of said are describing a helical pathwithin said annular space, the length of said annular space beinggreater than at least a major portion of the longitudinal distance saidarc travels in a half cycle, so that said arc is extinguished beforereaching the open end of said cavity.

References Cited in the file of this patent UNITED STATES PATENTS Re.21,087 Rankin May 16, 1939 1,784,303 Millikan et al. Dec. 9, 19302,027,836 Rankin et al Jan. 14, 1936 2,140,378 Biermanns et al Dec. 13,1938 2,411,892 Peters Dec. 5, 1946 FOREIGN PATENTS 594,282 Germany Mar.14, 1934 1,116,304 France Jan. 30, 1956

